1. Technical Field
This disclosure relates to a luminous unit for gas detection comprising a light source for linearly polarised light radiation and a housing with an exit window.
2. Discussion of Related Art
A gas sensor and an associated luminous unit are known from EP 1 783 481 A1. To improve the intensity stability it is proposed to tilt the exit window relative to the optical axis or main direction of radiation by the Brewster angle (in this case about 57°). Such a tilt, in linearly polarised laser light in pure p-polarisation, can reduce unwanted back-reflections at the cover.
However, there is still the problem that interference effects occur at the exit window which interfere with the signal that is to be measured. Disruptive optical modulations occur which are manifested for example as fluctuations in the light intensity measured as a function of the wavelength in the photodetectors of measuring apparatus for optical gas analysis. Particularly in an application known by the name “open path gas detection” (OPGD) in which the laser beam is passed over a shorter or longer distance through the space that is to be monitored, fluctuations in the radiation intensity are particularly disruptive as they significantly impair the signal-to-noise ratio. During measurement, in fact, it is generally not possible to distinguish directly between an attenuation caused by absorption in a gas and an attenuation caused by interference effects, which significantly increases the complexity of measurement that is to be carried out and the costs involved.
It would therefore be particularly desirable to provide a tunable luminous unit with a variable wavelength for gas detection in which the wavelength dependency of the light radiation intensity after the exit window is reduced.